It's what I thought, from a bundle (= liasse) of notarial deeds. Sometimes there is an index for them, but mostly they're just ordered by date.
An 'obligation' is a formal acknowledgement of debt, meaning generally a loan whose modalities are fixed and detailed through this deed legally recorded by the notaire (check http://en.wikipedia.org/wiki/Notaire#France
to understand how French notaires differ from usual civil-law notaries).
Here an example of an obligation deed (the date is later, but it shouldn't be very different): http://jose.chapalain.free.fr/pageprin1319.htm
I believe it is the monastery that loaned the 700 livres to your ancestor, not the contrary. Which also makes more sense unless he was a very rich landlord! Such a sum in the early 1700's is the equivalent of 3 little houses (count 200 livres for 1 fireplace, 2 doors, 2 windows) or 5/8 horses or oxes. A specialized worker would earn 1 or 2 livres by day, and a dowry between rich farmers is around 250 livres.
You can see here some prices for that period: http://morel.and.co.free.fr/mesures29.html
Makes me curious!
Try asking help from this benevolent service, they do search for notarial records (though limited to 1 request by month): http://www.francegenweb.org/~entraide/egwformu.php?dep=28